This invention generally relates to piston assemblies and to methods for manufacturing piston assemblies.
Piston assemblies are widely used in a variety of machines and other devices. One common use, for instance, is in a reciprocating compressor, employed as part of a refrigeration system, to compress a refrigerant vapor. Typically, a piston assembly includes a piston body, a connecting rod, and a wrist pin. The body defines a longitudinally extending recess, which is closed at a forward or head end, and a transverse piston bore, which intersects the longitudinal recess. A first end of the connecting rod extends into the longitudinal recess and defines a rod bore aligned with the transverse piston bore.
The wrist pin extends within this transverse piston bore and is supported by the piston body. The wrist pin also extends through the rod bore, joining the connecting rod to the piston body while allowing the connecting rod to pivot relative thereto. The connecting rod longitudinally extends from the wrist pin and, when assembled within a machine, a second or crankshaft end of the connecting rod is connected to an eccentric or off center portion of a rotatable crankshaft. Rotation of the crankshaft both pivots the connecting rod about the axis of the wrist pin and reciprocates the entire piston assembly. This reciprocating movement of the piston assembly may then be employed, as an example, to compress a vapor.
In these piston assemblies, it is usually preferred to secure the wrist pin within the piston bore defined by the piston body to prevent the wrist pin from inadvertently slipping out of the piston bore. Also, it is commonly preferred to maintain the connecting rod spaced from the sidewall of the piston body and to inhibit the connecting rod from sliding along the axis of the wrist pin. Maintaining the connecting rod spaced from the piston body sidewall prevents frictional wear between the connecting rod and the sidewall, increasing the effective life span of the connecting rod, the piston body, and thus the entire piston assembly. Preventing the connecting rod from sliding along the axis of the wrist pin inhibits cocking or bending of the connecting rod, further increasing the useful work life thereof.
For these reasons, piston assemblies are often provided with various clips, springs, or other similar members to hold the wrist pin within the piston bore and to maintain the forward end of the connecting rod centrally located along the axis of the wrist pin, spaced from the sidewall of the piston body. For example, the surfaces of the piston body that define the piston bore may also define a pair of spaced annular grooves extending around the piston bore, outward of the wrist pin. Snap rings may be fitted into these grooves and extend into the piston bore, axially outside the wrist pin to maintain wrist pin within the piston bore. In addition, spacing members may be disposed between the connecting rod and the piston sidewall, preventing the connecting rod from moving along the axis of the wrist pin and preventing contact between the connecting rod and the piston sidewall.
While these prior art retaining arrangements generally operate very effectively, they typically comprise a plurality of separate pieces or elements, and during the manufacture of the piston assembly, a separate step must be taken to place each individual piece within the piston assembly. Any reduction in the number of steps required to manufacture the piston assembly is, of course, highly desirable since it decreases the cost of the piston assembly and increases the productivity of the workers who manufacture these assemblies.